In this chapter, the methods of texture analysis, image quality evaluation, distance measures, univariate statistical analysis and the k-nearest-neighbor (kNN) classifier, which are used to evaluate despeckle filtering on ultrasound imaging and video, are presented. For speckle reduction, 16 different despeckle filtering methods, already described in [1,2], were applied to each image or video prior to intima-media complex (IMC) or atherosclerotic plaque segmentation. Despeckle filtering was applied after image or video normalization , either to the entire image or to an ROI, selected by the user. The selected area of interest (ROI) can be of any shape but the image despeckle filtering (IDF) software doesn't support multiple ROIs selection. In the latter case, where the user of the system is interested only in the selected ROI, the area outside the ROI can be blurred using the DsFlsmv filter operating with a sliding moving window of [15x15] pixels and a number iterations 5. It should be noted that the blurring is applied outside of the ROI if the user of the system is not interested to subjectively evaluate this area. The input parameters of the 16 different despeckle filters for the IDF and video despeckle filtering (VDF) software toolboxes can be selected by the user as it was documented in [1-4]. The 16 despeckle filters evaluated in this chapter were applied on a large number of asymptomatic (AS) and of symptomatic (SY) ultrasound images (220 vs 220) of the common carotid artery (CCA). Four despeckle filters (DsFlsmv, DsFhmedian, DsFkuwahara, DsFsrad) were further applied to ten videos of the carotid artery bifurcation. A large number of texture features (61 different texture features) were extracted from the original and despeckle images and videos, and the most discriminant ones are presented. The performance of these filters is investigated for discriminating between AS and SY images using the statistical kNN classifier. Moreover, 16 different image quality evaluation metrics were computed, as well as visual evaluation scores carried out by two experts.
A comparative evaluation on linear and nonlinear despeckle filtering techniques, Page 1 of 2
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